In recent years, with increased multifunctionality and operation speeds of information apparatuses such as personal computers and hard disk recorders, the amount of information handled by users has been increasing. Thus, the density with which an information recording apparatus records data to a recording medium has been desired to be increased. Increase in recording density requires miniaturization of a recording cell or mark that is a write unit for recording in the recording medium. However, for conventional recording media, miniaturization of recording cells or marks is confronted with serious challenges.
In recording media for current hard disk apparatuses, a granular thin film of thickness several tens of nanometers is deposited on a disk substrate. When grains in the granular thin film are miniaturized in order to increase the recording density, thermal fluctuation, i.e., a phenomenon in which a decrease in the volume of magnetic grains reduces the ratio of magnetic energy to thermal energy causing recording magnetization to change or disappear under the effect of temperature, occurs to make recording unstable in small polycrystals. Thus, although no problem occurs when the recording cells are large, recording may be unstable or noise increases when the recording cells are small. This is because the smaller recording cell contains a reduced number of crystal grains and contributes to relative increase in the level of the interaction between recording cells.
To avoid this problem, a bit pattered medium (BPM), which may be simply referred to as a patterned medium, has been proposed as a next-generation magnetic recording medium that replaces the thin film medium; in the bit patterned medium, a recording material is separated by a non-recording material in advance, and read and write are carried out using a single dot of recording material as a single recording cell.
The bit pattered medium includes a magnetic dot array with nanometer scale magnetic dots regularly arrayed on a substrate. A digital signal of “0” or “1”, where one dot corresponds to one bit, is recorded in the bit patterned medium depending on the direction of magnetization in each of the magnetic dots. In the bit patterned medium, the bits are physically completely isolated from one another. This in principle prevents possible noise resulting from magnetic transition, which is a major factor that hinders increase in the recording density of a continuous film medium.
However, the following problem is posed by the patterned medium in which the recording material is separated by the non-recording material on the surface of the recording medium. That is, a recording head needs to write data to each of the separated recording cells when recording the data in the recording medium at a particular position. Thus, adjusting timing when the recording head starts recording is important. If the recording is started at the wrong timing, the recording head may perform a write operation on the non-recording material or on the adjacent recording cells. This may result in an increase in the number of write errors.
In the bit patterned medium, the dots are arrayed in a square lattice pattern or a staggered pattern.
In the lattice pattern, in which the dots are aligned with one another lengthwise and crosswise, read and write are carried out using one dot row as one track. Thus, precise restrictive conditions are required for conditions in the cross track direction such as a head core width, tracking, and the like.
On the other hand, in the staggered pattern, which includes a large number of dot rows arranged at a given dot pitch, an odd numbered dot row is out of phase with a corresponding even numbered dot row by 180 degrees. When a head with a width covering two adjacent dot rows is utilized to carry out read and write using two dot rows as one data track, for example, the conditions in the cross track direction such as the head core width, tracking, and the like are relieved. However, if recording is carried out on the staggered pattern using two dot rows as one data track, a write phase margin decreases.
Thus, to increase the write phase margin, what is called shingled recording may be carried out in which the head records data in one dot row while moving in the cross track direction. However, a block configuration for error correcting codes (ECCs) is not taken into account in the shingled recording. Thus, the shingled recording has room for improvement in terms of efficient error correction and a data transfer rate.
Additionally, the shingled recording is applied not only to bit patterned media but also to continuous film media. Hence, the block configuration for the error correcting codes in the shingled recording needs to be taken into account for continuous film media.